Abnormal sympathetic signaling through adrenergic receptors is a major cause for many cardiovascular diseases, including heart failure, which is one of the leading health problems around the world. Sympathetic control is mediated mainly through norepinephrine, which signals via adrenergic receptors present on the surface of cardiac cells. Consistent with this, drugs targeting the adrenergic signaling pathway have been the mainstay for managing cardiovascular diseases and cardiac failure for many years. Adrenergic receptor activation initiates important regulatory events that cause their removal from the cell surface, which reduces cellular sensitivity to sympathetic stimuli. A critical sortin step in the endosome, which either recycles receptors back to the cell surface or directs them to be degraded, then decides whether and how fast cells recover their sensitivity. Recent evidence suggests that the sorting of receptors to specialized domains on the endosome that mediate recycling also allow receptors to interact with specialized signaling complexes and initiate signaling pathways with discrete functions. Research using prototypical G protein-coupled receptors (GPCRs) like the beta 2-adrenergic receptor (B2AR), has established that GPCRs require specific sequences on their C-termini, as well as a set of proteins that interact with thes sequences, to enter this pathway and recycle. Disrupting these interactions redirects B2AR to the lysosome. Why this is so, considering that many other proteins can recycle via a bulk recycling pathway without any apparent requirements, is a fundamental question that has not been answered. This proposal addresses how B2AR is excluded from the bulk recycling pathway, and why this is important in adrenergic signaling. The experiments test the hypothesis that specific endosomal machinery actively excludes B2AR from the bulk recycling pathway, and that this exclusion regulates the bias of B2AR signaling from the endosome vs. the plasma membrane. The approach taken is to first identify the machinery that excludes B2AR from the bulk pathway, and then disrupt it to determine the consequences on signaling. A better understanding of the mechanisms that regulate adrenergic receptor recycling will provide a platform for developing new therapeutic strategies against heart failure by identifying potential entry points for intervention. Further, as B2AR is a prototypical member of the G protein-coupled receptor family of signaling receptors, whose members show strong structural and functional similarities, the techniques developed and the principles identified will be broadly applicable to other members of this clinically relevant family of signaling receptors.